Patent GB-551306-A (GB)
Title: Improvements in or relating to variable pitch propeller control
IPC: B63H3/10
Filed: 1940-05-02
Abstract: 551,306. Fluid-pressure servomotor-control systems. STEVENS, A. H. (Hammond, jun., J. H.). May 2, 1940, No. 4265/41. Divided out of 551,302. [Class 135] [Also in Group XXXIII] In a system for maintaining under varying conditions a constant power output from the driving motor of a water or other craft, the pitch of the propeller blades is varied automatically by control mechanism responsive solely to changes in the temperature of the exhaust gases from the propeller driving motor. As shown, the pitch of the blades 13, which are driven from a Diesel engine 20 through a shaft 15, is controlled by a rod 19 passing through the shaft 15 and displaceable under the action of fluid acting upon a piston 27 in a cylinder 27a, the piston 27 being actuated by the displacement of fluid into a circuit comprising pump 26, valve 25, reservoir 36, distributor 25a and cylinder 27a. The position of the valve 25 is regulated by a motor 21 connected to the upper end of a floating lever 23, a central point of which is connected to a valve operating lever 24, and the lower end of which is associated with a sliding collar 29 movable in unison with the piston 27. The upper end of the lever 23 actuates by a wire 30 a propeller pitch-indicator 31, the reading of which corresponds with the position of the collar 29 and piston 27. The motor 21 is arranged in three alternative electric circuits including a battery 72, three-way switch 73, an adjustable rotatable disc incorporating contact segments 51 ... 56 and an insulating portion between the segments 53, 54, a pointer 44 connected to the centre contact of the switch 73, and resistances 66, 67, 70, 71 for providing a restoring current of desired magnitude. A thermo-element 41 in the exhaust pipe of the engine 20 determines the position of the pointer 44, while the disc 47 is rotated to its desired position by a hand-knob 50. The engine 20 is itself controlled by a constant-speed governor. In the operation of the device, the arm of the switch 73 is first moved on to its upper or lower contact to complete a circuit through the motor 21 and to adjust the pitch of the propellers as indicated at 31 to the desired value. The craft is next brought to its desired speed and at this stage the hand-knob 50 is rotated so that the insulation on disc 47 is brought below the pointer 44, and the arm of the switch 73 is moved to central position. Should the craft meet more adverse or more favourable conditions, the resistance to the propellers is increased or decreased, the temperature of the element 41 rises or falls with the increased or diminished output of the engine 20, and the pointer 44 moves on to one or other set of circuit-completing contacts 51-53 or 54 to 56, the motor 21 is driven at an appropriate speed to actuate the lever 23 and valve 25, the fluid circuit is put into operation and the piston 27 actuates the rod 19 to cause the requisite decrease or increase in the propeller pitch with a consequent restoration of the power output of the engine to normal. Following this, the temperature of the element 41. the pointer 44, motor 21, lever 23, collar 29 and indicator 31 in turn assume a fixed relation corresponding to the changed conditions encountered.